Printing using pyroelectric film

ABSTRACT

A method for printing using a pyroelectric material. A potentially pyroelectric material, whose dipoles can be oriented, is selectively and permanently poled to form a permanent pattern which corresponds to a graphic representation. The permanently, selectively poled material is heated or cooled, thereby forming a charge pattern corresponding to the graphic representation and toner powder placed on the material to form a pattern which can be transferred to a sheet of paper and fused thereto to form a printed page. The heating, toning, transfering and fusing can be repeated to print multiple copies.

United States Patent 1 Taylor PRINTING USING PYROELECTRIC FILM [75] Inventor: Allen L. Taylor, St. Paul, Minn.

[73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul, Minn.

[22] Filed: Aug. 6, 1973 [21] Appl. No.: 385,847

[52] US. Cl. 101/130; 96/1 R; 96/] LY; 96/1 SD; 96/1.4; 250/316; 307/88 ET;

[51] Int. Cl.... G03g 5/00; (303g 13/08; G03g 13/10 [58] Field of Search 1l7/17.5, 37 LE, 93.4; 96/] R, 1 LY, 1 SD, 1.4; 317/262 F; 307/88 ET; 250/316; 346/76 R, 74 ES [56] References Cited UNITED STATES PATENTS 3,276,031 9/1966 Gaynor 307/88 ET 3,364,020 11/1968 Fehlherg et al.. 307/88 ET 3,515,584 6/1970 Yang 1l7/17.5 3,519,461 7/1970 Stowell 117/l7.5 3,607,754 9/1971 Asahina et a1 307/88 ET [451 Aug. 19, 1975 3,660,736 5/1972 lgarashi et a1. 317/262 F 3,672,981 6/1972 Sloan et al. l17/l7.5

3,713,822 1/1973 Kiess 96/1 C 3,752,667 8/1973 DOnofrio 346/76 R 3,824,098 7/1974 Bergman et a1 96/1 C Primary ExaminerMichael Sofocleous Attorney, Agent, or FirmAleXander, Sell, Steldt & Delahunt [57] ABSTRACT A method for printing using a pyroelectric material. A potentially pyroelectric material, whose dipoles can be oriented, is selectively and permanently poled to form a permanent pattern which corresponds to a graphic representation.

The permanently, selectively poled material is heated or cooled, thereby forming a charge pattern corresponding to the graphic representation and toner powder placed on the material to form a pattern which can be transferred to a sheet of paper and fused thereto to form a printed page. The heating, toning, transfering and fusing can be repeated to print multiple copies.

11 Claims, 2 Drawing Figures PRINTING USING PYROELECTRHC FILM BACKGROUND OF THE INVENTION In one aspect this invention relates to pyroelectric materials. In a further aspect, this invention relates to pyroelectric polymeric film materials. In yet a further aspect, this invention relates to a method for printing using pyroelectric materials.

It is known that the dipoles ofa pyroelectric material, e.g., polyvinylidene fluoride film, which is biaxially oriented by the method of production, can be permanently poled by heating the material above a dipoleorienting temperature and then cooling the material in the presence of an electric field, see Bergman et al., Applied Physics Letters, Vol. 18, No. 5, Mar. 1, 1971.

Use of a system of lamp and lens to form a tempera ture image on a pyroelectric film has been disclosed, see Photoelectric Copying Process, Applied Physics Letters, Vol. 21, No. 10, Nov. 15, 1972, pp. 497 499. The resulting image can be used to copy by contacting the film with a charged ink which adheres to the electrostatic charge produced on the surface.

Also known is the use of a plurality of pyroelectricphotoconductive crystals on a supporting substrate to form copies. The crystals are exposed to a light source passed through a pattern forming a charge on the crys tals which is simultaneously drained away by the photoconductive effect. When the light source is removed a differential charge remains which will attract toner powder, see US. Pat. No. 3,713,822.

SUMMARY OF THE INVENTION Briefly, it has been found that pyroelectric materials, such as polyvinylidene fluoride film, can be used as printing masters. A portion of the material is permanently poled by heating the material and exposing it to an electric field which is varied in accordance with a pattern to be printed, the electric field being sufficiently strong to orient a portion of the dipoles in a configuration corresponding to the pattern. Conversely, the material can be selectively heated in accordance with the pattern to be printed and cooled in the presence of an electric field to orient the dipoles in accordance with the pattern.

The selectively and permanently poled film is heated above or cooled below ambient temperature to develop a charge pattern on the surface of the film corresponding to the dipole oriented pattern. The charge pattern will attract oppositely charged toner powder which can be transferred to paper or other suitable substrates and fused thereto using techniques well known in the art. The charge pattern can be repeatedly formed by heating or cooling the selectively and permanently poled film allowing the film to be used as a printing master for making as many copies as may be desired.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing:

FIG. 1 is a perspective view of one apparatus useful in the practice of this invention for selectively and permanently poling a pyroelectric material; and

FIG. 2 is a perspective view of an apparatus used according to the method of this invention to print using a selectively, permanently poled polymeric sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Normally the dipoles of a pyroelectric material are presented in a random fashion. When the pyroelectric material is heated above its poling temperature and an electric field applied, the dipoles are oriented. The material is then referred to as being poled. The degree of orientation or poling is a function of the materials temperature, the applied field strength, and the length of time the field is applied. For example, in polyvinylidene fluoride film, substantial poling begins when the film is heated to a temperature greater than C. and an electric field of about 4000 volts per millimeter of thickness is applied for 15 minutes while the film is above this temperature. Increasing the temperature and/or the applied field will increase the degree of poling until the film is saturated. Once the poled film is cooled below the poling temperature, the field may be removed and the dipoles will remain oriented. Care should be taken to avoid reheating the permanently poled sheet to a temperature above its poling temperature which will randomize the dipoles.

The pyroelectric polymeric materials to be permanently poled can be heated by various means well known in the art. Among the heating means contemplated in the use of this invention are hot oil baths, warm air ovens, lamps, electromagnetic radiation, electron beams, etc. The heat can be applied to a material which is stationary or moving relative to the heat source.

The electric field used to orient the dipoles can be applied in a variety of ways, i.e. flat metal contacts, c0- rona, pointed metal contacts, electromagnetic radiation, etc.

The permanent poling can be selectively applied by the application of a variable electrical potential to the heated pyroelectric polymeric material, such electrical potential being varied in accordance with the pattern to be copied. Various means, such as shaped electrodes, can be used to accomplish the poling, the normal poling potential being in the range of 50,000 to 100,000 volts per millimeter of thickness. In the alternative, it is possible to selectively and permanently pole a pyroelectric material by applying a constant field and selectively heating the material.

The selectively, permanently poled polymeric film can be used to form multiple copies representative of the selective poling. The selectively, permanently poled film is subjected to a change in temperature which may be conveniently accomplished by a heat source such as a radiant heating element. The change in temperature induces a charge pattern on the films surface representative of the selective poling since the charge formed is proportional to the degree and the magnitude of the temperature change of poling. A sequence of steps such as cooling, neutralizing and heating, or heating, neutralizing and cooling can also be used to form a charge pattern. Such a sequence of steps permits toning at ambient temperature.

After a charge pattern has been induced on the films surface by heating or cooling, the films surface is contacted with charged toner particles which adhere to oppositely charged portions of the films surface. The amount of toner which adheres to the film is dependent on the magnitude of the induced charge, which, as

mentioned, varies directly with the degree of poling present.

The toner particles adhering to the film can be transferred to a suitable copy material, e.g., a sheet of paper using techniques well known in the art. The process of heating the selectively, permanently poled material, contacting the heated material with charged toner particles, and transferring the particles from the poled material to a copy material can be repeated until the de sired number of copies has been printed.

The selectively, permanently poled pyroelectric material thus provides a permanent master. Accordingly. the method described is considered a method for printing in that multiple copies are made from a permanent master as opposed to a method for copying where for each copy it is necessary to use the original pattern to be copied.

The method will be described in greater detail in connection with FIGS. 1 and 2. A sheet of pyroelectric material 12 is placed between electrodes l4, l6, electrode 16 being transparent with respect to light. A graphic pattern 18 is placed between pyroelectric material 12 and light source 20 so that the pyroelectric material is selectively heated. A voltage is applied across pyroelectric material 12 while it is heated and the pyroelectric material then allowed to cool with the field applied to selectively and permanently pole the pyroelectric material 12 in accordance with graphic pattern 18.

The selectively and permanently poled material 12 can be used to print numerous copies of the original graphic representation, one example of a suitable apparatus being shown in FIG. 2. The selectively and permanently poled sheet 12 is attached to rotatable drum 24, and the apparatus positioned so a portion of poled sheet 12 is in toner solution 30. The drum 24 is connected to ground potential. As drum 24 is turned counterclockwise any charges on the surface of sheet 12 are removed by neutralizer 26 which may, for example, be an alpha particle eliminator. Sheet 12 is then heated by heating means 28 to develop-a charge pattern on the surface of the sheet. The charge pattern so produced will be in accordance with the selective, permanent poling that was produced earlier. The sheet 12 is then passed into toner solution 30 containing charged particles 32, the particles being attracted to the sheet 12 in proportion to the charge presented by the charge pattern. The particles are transferred to a suitable copy material, e.g., a sheet of paper, and the particles fused to the material by suitable means well known in the art. This transfer may be accomplished with the apparatus of FIG. 2 wherein a sheet of paper 34 for receiving the charged particles 32 attracted to the sheet 12 is carried on a drum 36 which rotates clockwise as drum 24 is moved counter-clockwise. Only the steps following the selective and permanent poling of the material 12 need be repeated for each copy that is desired.

A further understanding may be had by referring to the following nonlimiting examples. It is to be understood that the invention is not limited to the illustrative embodiments set forth herein.

EXAMPLE 1 A sheet of2 mil (0.05 mm.) biaxially oriented polyvi nylidene fluoride film 5 inches by 12 inches (about 12.7 cm. by 30.5 cm.) was poled by: heating the sheet to 150C. in a mineral oil bath, impressing a field of +3000 volts in one area and 3000 volts in another area by means of copper electrodes. then cooling the bath to 50C. with the fields applied. The sheet was Finally cooled to room temperature.

One side of the sheet was grounded and an alpha particle eliminator used to neutralize any extraneous charges on the ungrounded side. The neutralized sheet was dipped into a toner solution, (Graphofax", a trademarked product of Dennison), maintained at 55C. The elevated temperature (55C.) developed a negative charge in the areas poled by the 3000 Volt field.

The sheet with the toner particles was removed from the toner solution and the toner particles transferred to an adhesive coating giving a print of the electrode pattern.

When the toner solution was cooled below room temperature to 10C. the poled areas exposed to the +3000 volt field developed a negative charge which attracted the toner particles.

Thus a printing master can be made on pyroelectric film which can be used to print images formed by selectively poling of the pyroelectric film using different electric fields.

EXAMPLE 2 A web of polyvinylidene fluoride 0.05 millimeter thick and 6.25 millimeters wide was poled by passing the sheet into a divided oil bath. The hot oil was maintained at C. and the cool oil bath at 35C. The film moved through the hot oil and between two flat electrodes where a sinusoidal varying frequency electric field was applied, the voltage ranging from 3000 to 8000 volts and then into the cooler oil forming a permanently, differentially poled material.

One side of the permanently poled material was aerosol coated with a silver film and grounded.

The sample was heated about 30C. above room temperature, neutralized using a conductive brush (available as a Pluton brush) and the sample cooled. The resulting sheet had a selective charge pattern corresponding to the variations in the electric field, the higher charges corresponding to the higher field potential and vice versa.

The charge pattern formed faithfully reproduced the wave form used and decayed less than 10 percent in several (3 4) hours.

The selective charge pattern was developed by placing the sheet with its charges in the liquid toner solution of Example 1 at room temperature. The charged toner particles were attracted to the selective charge pattern. The toner particles were transferred to a sheet of paper and fused to the paper at C. to form a printed copy of the original pattern.

A second method of developing the selective charged pattern was used. An elastomeric roller with permanent magnets inside was coated with electrically charged magnetic toner particles. As the roller was moved over the sheet the charge pattern attracted the charged particles developing the pattern. The particles were transferred to paper and fused above.

EXAMPLE 3 A circular 12 cm. diameter by 0.05 cm. thick piece of ceramic lanthanum doped lead-zirconate-titanate having a composition of 57 weight percent lead zirconate, 31 percent lead titanate and 12 weight percent lanthanum was formed.

A striped pattern of silver electrodes was painted on one surface of the electrode and a ground electrode formed on the opposite surface.

The sample was heated to 200C, a field of 4000 volts applied to the strip electrodes, and the sample cooled in the presence of the applied field to room temperature.

The strip electrodes were removed and the selec tively, permanently poled ceramic disc was placed in the toner solution of Example 1 which had been warmed to 50C. with the ground electrode connected to ground. The heat formed a striped charge pattern on the ceramic disc which attracted the charged toner particles.

What is claimed is:

l. A method for printing an image pattern using a permanent master provided by a selectively, permanently poled pyroelectric material comprising the steps of:

l. heating a pyroelectric material to a poling temperature and exposing the heated material to an electric field, the combination of electric field and heat being applied to only selected portions of the pyroelectric material in accordance with an image pattern to be printed;

2. cooling said pyroelectric material to a temperature below said poling temperature while maintaining said electric field whereby the pyroelectric material is selectively, permanently poled in accordance with the image pattern to be printed;

3. heating the poled material uniformly to develop a charge pattern in accordance with the selective poling present in the material;

4. contacting the heated film with charged toner particles which are attracted to the pyroelectric material in accordance with the charge pattern;

5. placing a suitable copy substrate in registry on the material and toner to transfer said toner from said material to said copy substrate;

6. fusing said toner to said copy substrate; and repeating the steps after step 2 to form the desired number of copies.

2. The method of claim 1, where said pyroelectric material is polymeric film.

3. The method of claim 2, where said film is polyvinylidene fluoride.

4. The method of claim 1, where said pyroelectric material is lead-zirconatetitanate.

5. The method of claim 1, where said heating step is carried out by use of a radiant heat source.

6. The method of claim 1, comprising the additional steps of cooling the poled material; and neutralizing the charge produced prior to step 3.

7. A method for printing using a permanent master provided by a selectively, permanently poled pyroelectric material comprising the steps of:

1. heating a pyroelectric material to a poling temperature and exposing the heated material to an electric field, the combination of electric field and heat being applied to only selected portions of the pyroelectric material in accordance with an image pattern to be printed;

2. cooling said pyroelectric material to a temperature below said poling temperature while maintaining said electric field whereby the pyroelectric material is selectively, permanently poled in accordance with the image pattern to be printed;

3. cooling the poled material uniformly to develop a charge pattern in accordance with the selective poling present in the material;

4. contacting the cooled film with charged toner particles which are attracted to the material in accordance with the charge pattern;

5. placing a suitable copy substrate in registry on the material and toner to transfer said toner from said material to said copy substrate;

6. fusing said toner to say copy substrate; and repeating the steps after step 2 to form the desired number of copies.

8. The method of claim 7, where said pyroelectric material is polymeric film.

9. The method of claim 8, where said film is polyvinylidene fluoride.

10. The method of claim 7, where said pyroelectric material is lead-zirconate-titanate.

11. The method of claim 7, comprising the additional steps of heating the poled material; and

neutralizing the charge produced prior to step 3. 

1. A METHOD FOR PRINTING AN IMAGE PATTERN USING A PERMANENT MASTER PROVIDED BY A SELECTIVELY PERMANENTLY POLED PYROELECTRIC MATERIAL COMPRISING THE STEPS OF:
 1. HEATING A PYROELECTRIC MATERIAL TO A POLING TEMPERATURE AND EXPOSING THE HEATED MATERIAL TO AN ELECTRIC FIELD, THE COMBINATION OF ELECTRIC FIELD AND HEAT BEING APPLIED TO ONLY SELECTED PORTION OF THE PYROELECTRIC MATERIAL IN ACORDANCE WITH AN IMAGE PATTERN TO BE PRINTED,
 2. COOLING SAID PYROELECTRIC MATERIAL TO A TEMPERATURE BELOW SAID POLING TEMPERATURE WHILE MAINTAINING SAID ELECTRIC FIELD WHEREBY THE PYROELECTRIC MATERIAL IS SELECTIVELY, PERMANENTLY POLED IN ACCORDANCE WITH THE IMAGE PATTERN TO BE PRINTED,
 2. cooling said pyroelectric material to a temperature below said poling temperature while maintaining said electric field whereby the pyroelectric material is selectively, permanently poled in accordance with the image pattern to be printed;
 2. The method of claim 1, where said pyroelectric material is polymeric film.
 2. cooling said pyroelectric material to a temperature below said poling temperature while maintaining said electric field whereby the pyroelectric material is selectively, permanently poled in accordance with the image pattern to be printed;
 3. cooling the poled material uniformly to develop a charge pattern in accordance with the selective poling present in the material;
 3. The method of claim 2, where said film is polyvinylidene fluoride.
 3. heating the poled material uniformly to develop a charge pattern in accordance with the selective poling present in the material;
 4. contacting the heated film with charged toner particles which are attracted to the pyroelectric material in accordance with the charge pattern;
 3. HEATING THE POLED MATERIAL UNIFORMLY TO DEVELOP A CHARGE PATTERN IN ACCORDANCE WITH THE SELECTIVE POLING PRESENT IN THE MATERIAL,
 4. CONTACTING THE HEATED FILM WITH CHARGED TONER PARTICLES WHICH ARE ATTRACTED TO THE PYROELECTRIC MATERIAL IN ACCORANCE WITH THE CHARGE PATTERN,
 4. The method of claim 1, where said pyroelectric material is lead-zirconate-titanate.
 4. contacting the cooled film with charged toner particles which are attracted to the material in accordance with the charge pattern;
 5. The method of claim 1, where said heating step is carried out by use of a radiant heat source.
 5. PLACING A SUITABLE COPY SUBSTRATE IN REGISTRY ON THE MATERIAL AND TONER TO TRANSFER SAID TONER FROM SAID MATERIAL TO SAID COPY SUBSTRATE,
 5. placing a suitable copy substrate in registry on the material and toner to transfer said toner from said material to said copy substrate;
 5. placing a suitable copy substrate in registry on the material and toner to transfer said toner from said material to said copy substrate;
 6. fusing said toner to say copy substrate; and repeating the steps after step 2 to form the desired number of copies.
 6. fusing said toner to said copy substrate; and repeating the steps after step 2 to form the desired number of copies.
 6. FUSING SAID TONER TO SAID COPY SUBSTRATE AND REPEATING THE STEPS AFTER STEP 2 TO FORM THE DESIRED NUMBER OF COPIES.
 6. The method of claim 1, comprising the additional steps of cooling the poled material; and neutralizing the charge produced prior to step
 3. 7. A method for printing using a permanent master provided by a selectively, permanently poled pyroelectric material comprising the steps of:
 8. The method of claim 7, where said pyroelectric material is polymeric film.
 9. The method of claim 8, where said film is polyvinylidene fluoride.
 10. The method of claim 7, where said pyroelectric material is lead-zirconate-titanate.
 11. The method of claim 7, comprising the additional steps of heating the poled material; and neutralizing the charge produced prior to step
 3. 